Messages in this thread Patch in this message | | | From | Jungseok Lee <> | Subject | [PATCH v3] arm64: Introduce IRQ stack | Date | Tue, 22 Sep 2015 12:11:58 +0000 |
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Currently, kernel context and interrupts are handled using a single kernel stack navigated by sp_el1. This forces a system to use 16KB stack, not 8KB one. This restriction makes low memory platforms suffer from memory pressure accompanied by performance degradation.
This patch addresses the issue as introducing a separate percpu IRQ stack to handle both hard and soft interrupts with two ground rules:
- Utilize sp_el0 in EL1 context, which is not used currently - Do not complicate current_thread_info calculation
It is a core concept to directly retrieve struct thread_info from sp_el0. This approach helps to prevent text section size from being increased largely as removing masking operation using THREAD_SIZE in tons of places.
[Thanks to James Morse for his valuable feedbacks which greatly help to figure out a better implementation. - Jungseok]
Tested-by: James Morse <james.morse@arm.com> Signed-off-by: Jungseok Lee <jungseoklee85@gmail.com> --- Changes since v2: - Optmised current_thread_info function as removing masking operation and volatile keyword per James and Catalin - Reworked irq re-enterance check logic using top-bit comparison of stacks per James - Added sp_el0 update in cpu_resume per James - Selected HAVE_IRQ_EXIT_ON_IRQ_STACK to expose this feature explicitly - Added a Tested-by tag from James - Added comments on sp_el0 as a helper messeage
Changes since v1: - Rebased on top of v4.3-rc1 - Removed Kconfig about IRQ stack, per James - Used PERCPU for IRQ stack, per James - Tried to allocate IRQ stack when CPU is about to start up, per James - Moved sp_el0 update into kernel_entry macro, per James - Dropped S_SP removal patch, per Mark and James
arch/arm64/Kconfig | 1 + arch/arm64/include/asm/irq.h | 2 + arch/arm64/include/asm/thread_info.h | 10 ++++- arch/arm64/kernel/entry.S | 35 +++++++++++++--- arch/arm64/kernel/head.S | 5 +++ arch/arm64/kernel/irq.c | 21 ++++++++++ arch/arm64/kernel/sleep.S | 3 ++ arch/arm64/kernel/smp.c | 6 +++ 8 files changed, 76 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 07d1811..9767bd9 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -68,6 +68,7 @@ config ARM64 select HAVE_FUNCTION_GRAPH_TRACER select HAVE_GENERIC_DMA_COHERENT select HAVE_HW_BREAKPOINT if PERF_EVENTS + select HAVE_IRQ_EXIT_ON_IRQ_STACK select HAVE_MEMBLOCK select HAVE_PATA_PLATFORM select HAVE_PERF_EVENTS diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h index bbb251b..ba12725 100644 --- a/arch/arm64/include/asm/irq.h +++ b/arch/arm64/include/asm/irq.h @@ -10,6 +10,8 @@ struct pt_regs; extern void migrate_irqs(void); extern void set_handle_irq(void (*handle_irq)(struct pt_regs *)); +extern int alloc_irq_stack(unsigned int cpu); + static inline void acpi_irq_init(void) { /* diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h index dcd06d1..fa014df 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -71,10 +71,16 @@ register unsigned long current_stack_pointer asm ("sp"); */ static inline struct thread_info *current_thread_info(void) __attribute_const__; +/* + * struct thread_info can be accessed directly via sp_el0. + */ static inline struct thread_info *current_thread_info(void) { - return (struct thread_info *) - (current_stack_pointer & ~(THREAD_SIZE - 1)); + unsigned long sp_el0; + + asm ("mrs %0, sp_el0" : "=r" (sp_el0)); + + return (struct thread_info *)sp_el0; } #define thread_saved_pc(tsk) \ diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 4306c93..e5b8482 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -88,7 +88,8 @@ .if \el == 0 mrs x21, sp_el0 - get_thread_info tsk // Ensure MDSCR_EL1.SS is clear, + mov tsk, sp + and tsk, tsk, #~(THREAD_SIZE - 1) // Ensure MDSCR_EL1.SS is clear, ldr x19, [tsk, #TI_FLAGS] // since we can unmask debug disable_step_tsk x19, x20 // exceptions when scheduling. .else @@ -105,6 +106,7 @@ .if \el == 0 mvn x21, xzr str x21, [sp, #S_SYSCALLNO] + msr sp_el0, tsk .endif /* @@ -164,8 +166,28 @@ alternative_endif .endm .macro get_thread_info, rd - mov \rd, sp - and \rd, \rd, #~(THREAD_SIZE - 1) // top of stack + mrs \rd, sp_el0 + .endm + + .macro irq_stack_entry + adr_l x21, irq_stack + mrs x22, tpidr_el1 + add x21, x21, x22 + ldr x22, [x21] + and x21, x22, #~(THREAD_SIZE - 1) + mov x23, sp + and x23, x23, #~(THREAD_SIZE - 1) + cmp x21, x23 // check irq re-enterance + mov x21, sp + csel x23, x21, x22, eq // x22 = top of irq stack + mov sp, x23 + .endm + + /* + * x21 is preserved between irq_stack_entry and irq_stack_exit. + */ + .macro irq_stack_exit + mov sp, x21 .endm /* @@ -183,10 +205,11 @@ tsk .req x28 // current thread_info * Interrupt handling. */ .macro irq_handler - adrp x1, handle_arch_irq - ldr x1, [x1, #:lo12:handle_arch_irq] + ldr_l x1, handle_arch_irq mov x0, sp + irq_stack_entry blr x1 + irq_stack_exit .endm .text @@ -597,6 +620,8 @@ ENTRY(cpu_switch_to) ldp x29, x9, [x8], #16 ldr lr, [x8] mov sp, x9 + and x9, x9, #~(THREAD_SIZE - 1) + msr sp_el0, x9 ret ENDPROC(cpu_switch_to) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 90d09ed..dab089b 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -441,6 +441,9 @@ __mmap_switched: b 1b 2: adr_l sp, initial_sp, x4 + mov x4, sp + and x4, x4, #~(THREAD_SIZE - 1) + msr sp_el0, x4 // Save thread_info str_l x21, __fdt_pointer, x5 // Save FDT pointer str_l x24, memstart_addr, x6 // Save PHYS_OFFSET mov x29, #0 @@ -618,6 +621,8 @@ ENDPROC(secondary_startup) ENTRY(__secondary_switched) ldr x0, [x21] // get secondary_data.stack mov sp, x0 + and x0, x0, #~(THREAD_SIZE - 1) + msr sp_el0, x0 // save thread_info mov x29, #0 b secondary_start_kernel ENDPROC(__secondary_switched) diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c index 11dc3fd..5272bfd 100644 --- a/arch/arm64/kernel/irq.c +++ b/arch/arm64/kernel/irq.c @@ -31,6 +31,8 @@ unsigned long irq_err_count; +DEFINE_PER_CPU(void *, irq_stack); + int arch_show_interrupts(struct seq_file *p, int prec) { show_ipi_list(p, prec); @@ -50,6 +52,9 @@ void __init set_handle_irq(void (*handle_irq)(struct pt_regs *)) void __init init_IRQ(void) { + if (alloc_irq_stack(smp_processor_id())) + panic("Failed to allocate IRQ stack for boot cpu"); + irqchip_init(); if (!handle_arch_irq) panic("No interrupt controller found."); @@ -115,3 +120,19 @@ void migrate_irqs(void) local_irq_restore(flags); } #endif /* CONFIG_HOTPLUG_CPU */ + +int alloc_irq_stack(unsigned int cpu) +{ + void *stack; + + if (per_cpu(irq_stack, cpu)) + return 0; + + stack = (void *)__get_free_pages(THREADINFO_GFP, THREAD_SIZE_ORDER); + if (!stack) + return -ENOMEM; + + per_cpu(irq_stack, cpu) = stack + THREAD_START_SP; + + return 0; +} diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S index f586f7c..e33fe33 100644 --- a/arch/arm64/kernel/sleep.S +++ b/arch/arm64/kernel/sleep.S @@ -173,6 +173,9 @@ ENTRY(cpu_resume) /* load physical address of identity map page table in x1 */ adrp x1, idmap_pg_dir mov sp, x2 + /* save thread_info */ + and x2, x2, #~(THREAD_SIZE - 1) + msr sp_el0, x2 /* * cpu_do_resume expects x0 to contain context physical address * pointer and x1 to contain physical address of 1:1 page tables diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index dbdaacd..0bd7049 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -97,6 +97,12 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) secondary_data.stack = task_stack_page(idle) + THREAD_START_SP; __flush_dcache_area(&secondary_data, sizeof(secondary_data)); + ret = alloc_irq_stack(cpu); + if (ret) { + pr_crit("CPU%u: failed to allocate IRQ stack\n", cpu); + return ret; + } + /* * Now bring the CPU into our world. */ -- 2.5.0
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